1. Field of the Invention
The present invention relates to a fluid pressure boosting type brake system comprising a fluid pressure source including a fluid pump and a pressure tank connected to the pump, and a control valve capable of controlling an output pressure from the fluid pressure source to a fluid pressure corresponding to a degree brake of operation to output the same.
2. Description of the Related Art
Such brake systems are already known, for example, from Japanese Patent Application Laid-open Nos. 274958/92 and 345568/92.
In the brake system disclosed in Japanese Patent Application Laid-open No. 274958/92, the operation of the fluid pump is controlled by a pressure switch which is turned ON, when the fluid pressure in the pressure tank becomes equal to or less than a predetermined value. Therefore, when the pressure switch malfunctions, the fluid pump may not be operated, resulting in a reduction in brake assisting force. In the brake system disclosed in Japanese Patent Application Laid-open No. 345568/92, the fluid pressure in the pressure tank is detected by a pressure sensor in addition to the pressure switch, thereby judging whether or not the pressure switch is normal. However, if a circuit for controlling the operation of the fluid pump, under reception of the detection values detected by the pressure switch and the pressure sensor, malfunctions, then the fluid pump may fail to be operated, resulting in a reduction in brake assisting force.